Now, Simon Tremain has been fined $750 and censured by the Real Estate Agents Authority for unsatisfactory conduct over the 2009 sale of the house. This included failing to disclose he was a joint owner and that the downstairs studio was water damaged.

Both he and the angry new owners, Gavin and Jenny Burgess, are appealing the ruling. Simon Tremain thinks it was too severe; they think it wasn't harsh enough.

Chris Tremain has since resigned his directorship on being appointed to Cabinet in April. But he told the Herald on Sunday earlier this year that he still had an interest in the company, thought to be through a shareholding held in trust.

The Burgesses want the Tremains to fix walls in the rotting home they had hoped would be their idyllic weekend bolthole, and are seeking mediation before taking their long-running dispute to the Weathertight Homes Tribunal.

An independent engineer's report has estimated it will cost more than $22,000 to seal a leaky concrete wall, but there are no guarantees this will fix the problem.

Yesterday, an apologetic Simon Tremain took full responsibility for the unresolved leak and permit issues, telling the Herald on Sunday that, in hindsight, the sale had become "a little too personal for me".

"I take full responsibility for it and am dealing with the issues to sort it out."

Tremain, who has since bought another property in the bush-clad Waipatiki settlement, said he got emotional at the time and should have stepped aside. He insisted his politician brother had nothing to do with the sale, despite his shared ownership of the house and company.

Jenny Burgess said she was pleased Tremain was admitting responsibility.

The leaks had been exposed after a particularly long, wet miserable winter. "Sometimes it was a bit like a stream," she said.

Sodden mattresses had to be thrown out and saturated mouldy walls wiped down frequently, but she was told by Simon Tremain that had never happened before.

In the meantime the couple, who lived in the upstairs studio, continued to use the rotting downstairs bedrooms, converted from an boat shed built in the 60s, for visiting family.

But the situation was far from ideal. "It's embarrassing. It's put a big blemish on our beautiful home."

Cabinet Minister Chris Tremain did not respond to messages last night, and was said to be overseas. His press secretary Mary-Jane Rendle refused to comment.